if (redis.call("exists",KEYS[1])==1) then
    local stock = tonumber(redis.call("get",KEYS[1]));
    if (stock>0) then
        redis.call("incrby",KEYS[1],-1);
        return stock;
    end;
    return 0;
end;

-- if (redis.call("exists", KEYS[1]) == 1) then
--     local stock = redis.call("incrby", KEYS[1], -1);
--     return stock;
-- end;